1. Field of the Invention
This invention relates to a protective coating formed over a dielectric layer, used for electrostatically clamping a semiconductor wafer to a wafer support in integrated circuit processing apparatus, to protect the dielectric layer from chemical attack; and the method of protecting the dielectric layer.
2. Description of the Related Art
In the processing of semiconductor wafers in a sealed chamber to form integrated circuit structures thereon, the semiconductor wafer is normally positioned on a wafer support within the chamber. To secure the wafer to the support, and in particular to prevent movement of the wafer (either vertically or laterally) during processing, it has been customary to physically clamp the wafer to the underlying support.
More recently however, other means for securing the wafer to the support have been explored and adopted due to various problems, such as particle formation, mechanical stress, etch profiles, etc., which have been experienced with the use of mechanical force to secure the wafer to the support.
One such wafer securement means, commonly referred to as electrostatic clamping, utilizes an electrostatic charge on the surface of a dielectric material formed over the portion of the metal wafer support facing the wafer, i.e., between the undersurface of the wafer and the facing surface of the underlying metal wafer support. Such electrostatic clamping is described, for example, in Abe U.S. Pat. No. 4,384,918; Japan Patent Document 2-27748; and in "Electrostatic Force and Absorption Current of Alumina Electrostatic Chuck", published by Watanabe et al. in Jpn. Journal of Applied Physics, Vol. 31 (1992) at pages 2145-2150.
While this type of wafer securement, utilizing electrostatic clamping, has proved to be successful in eliminating the previous problems encountered in the mechanical clamping of the wafer to the wafer support, corrosion problems have been encountered because the dielectric materials which provide the most satisfactory performance in the use of electrostatic clamping to secure the wafer to the wafer support do not exhibit sufficient resistance to some of the chemicals used during the processing of the semiconductor wafer in the chamber.
In particular, when a polyimide material is provided, as the dielectric material, on the top surface of the metal wafer support, it has been found that such polyimide material is susceptible to chemical attack by O.sub.2 gas, used for in situ cleaning of the chamber after etching. The polyimide material has also been found to be subject to chemical attack by fluorine-containing gases as well, although to a lesser extent than the vulnerability to O.sub.2 attack.
It therefore would be desirable to provide protection against chemical attack for the dielectric material, formed on the surface of the metal wafer support for the purpose of electrostatic clamping of a semiconductor wafer to the wafer support, without however, interfering with the electrostatic charge on the surface of the dielectric material.